Sojourn Times in the M/PH/1 Processor Sharing Queue

  • Authors:
  • Bruno Sericola;Fabrice Guillemin;Jacqueline Boyer

  • Affiliations:
  • INRIA-IRISA, Campus de Beaulieu, Rennes, France 35042;Division R&D, France Telecom, Lannion, France 22300;Division R&D, France Telecom, Lannion, France 22300

  • Venue:
  • Queueing Systems: Theory and Applications
  • Year:
  • 2005

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Abstract

We give in this paper an algorithm to compute the sojourn time distribution in the processor sharing, single server queue with Poisson arrivals and phase type distributed service times. In a first step, we establish the differential system governing the conditional sojourn times probability distributions in this queue, given the number of customers in the different phases of the PH distribution at the arrival instant of a customer. This differential system is then solved by using a uniformization procedure and an exponential of matrix. The proposed algorithm precisely consists of computing this exponential with a controlled accuracy. This algorithm is then used in practical cases to investigate the impact of the variability of service times on sojourn times and the validity of the so-called reduced service rate (RSR) approximation, when service times in the different phases are highly dissymmetrical. For two-stage PH distributions, we give conjectures on the limiting behavior in terms of an M/M/1 PS queue and provide numerical illustrative examples.